Revolvers are primarily designed to accommodate rimmed cartridges, that is, cartridges which have a terminal rim that is larger in diameter than the diameter of the cartridge body. The rim is provided for at least partially engaging a wall of the rotating cylinder, with part of the rim received by an extractor mechanism. A typical extractor mechanism has a head for engaging the rim portion of each cartridge disposed within the chambers of the cylinder so that after the cylinder is swung out to its loading/unloading position, the extractor is pushed back with the head engaging the rim displacing the cartridges rearwardly so that all the cartridges are ejected simultaneously.
In contrast, the cartridges used in automatic pistols are rimless, that is, they have heads with an inward groove so that the heads are approximately the same diameter as the body of the cartridge. Rimmed shells or cartridges are the standard for use with revolvers. Rimless shells or cartridges are the standard for use with semi-automatic pistols.
A revolver has several advantages over semi-automatic hand guns. For example, semi-automatic hand guns must be “cocked” in order to chamber a first round in the firing breech. After the gun has been cocked, it will fire every time the trigger is pulled, i.e. with a single action, which also results in automatic discharge of the spent shell casing. Automatic pistols have a certain inherent risk, as once cocked, should the safety switch be disengaged accidentally, the gun could unintentionally discharge.
A revolver on the other hand requires a trigger pull and hammer retraction, i.e., a double action is required for discharge. Thus, a revolver which does not have to be cocked before firing, is a safer weapon, and as such, is often used as a back-up weapon by military and law enforcement personnel. However, in spite of the safety factor, the use of revolvers has been limited by the requirement of having to carry two types of ammunition, rimless cartridges for the main weapon, and rimmed cartridges for the back-up weapon.
It is quite inconvenient and expensive to maintain stocks of both rimmed and rimless ammunition, particularly when the ammunition is of the same caliber.
As the use of rimless cartridges has proliferated, efforts have been made to modify revolvers to allow utilization of rimless ammunition. In U.S. Pat. No. 4,541,193, a revolver cylinder has a central longitudinal chamber, a plurality of longitudinal cartridge chambers and radial slots at the rear of each cartridge receiving cylinder for communicating between the central chamber and each cartridge chamber. An ejector assembly disposed in the central chamber has a plurality of radial projections disposed at the end of extraction fingers which engage the grooves of each rimless cartridge. However, the size of the ejector components requires a relatively large central bore, which can reduce cylinder strength.
In U.S. Pat. No. 4,015,356, spring clips are used to retain rimless cartridges in a revolver cylinder. However, these are prone to breakage and jamming, and so have not gained wide acceptance.
In U.S. Pat. Nos. 4,127,955, 4,934,082 and 5,341,587, various spring fingers are disclosed for use in adapting a revolver cylinder for receiving and ejecting rimless cartridges. However, these still suffer from problems of uniform discharge and ejection, and possible reduction of cylinder strength, and so, generally, none of these solutions has gained wide acceptance in the industry.
Other background related information on revolvers and extractors can be found in U.S. Pat. Nos. 3,982,346 and 4,577,429.
What is needed is a low cost yet reliable cylinder assembly which includes an extractor mechanism that will permit use of rimless cartridges in revolvers without requiring a large central bore that could reduce cylinder strength. It is also desired to have a cylinder assembly which includes an extractor mechanism that is sufficiently robust so as to avoid jamming and breakage for the life of the revolver.